Silane treated inorganic pigments

ABSTRACT

The present invention provides a process for the production of hydrophobic inorganic oxide products which comprises reacting the inorganic oxide particles with organohalosilanes, preferably organochlorosilanes, to produce hydrophobic organosilane coated inorganic oxides. It is preferred that the organohalosilane compounds be reacted with the inorganic oxide particles in an aqueous slurry and subjected to intense mixing. The inorganic oxide pigments prepared by the processes of this invention have essentially quantitative retention of the organosilanes and contain no adsorbed aldehydes on their surface. The by-products produced in the preferred embodiments of the invention are innocuous salts, which are environmentally safe and readily disposable.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application U.S.application Ser. No. 08/565,852, filed Dec. 1, 1995, now U.S. Pat. No.5,653,794 the contents of which are hereby incorporated by referenceinto the present disclosure.

BACKGROUND OF THE INVENTION

The present invention relates to hydrophobic, surface modified,inorganic metal oxide pigments, such as titanium dioxide (TiO₂)pigments, which are substantially free of aldehydes and otherpotentially volatile organic compounds on their surface. The inventionalso relates to an improved, environmentally safer method for thepreparation of such pigments and to polymers containing such pigments.

Titanium dioxide is the premier white pigment used for whitening,brightening and opacifying paper, paints and plastics. As normallyproduced, TiO₂ is a hydrophilic pigment, meaning that it is readily wetby water and not wet by hydrophobic materials like organic polymers. Inorder to permit TiO₂ pigments to be wet-out by and dispersed in organicpolymers, the surface of the pigment must be modified, or madehydrophobic, so that the polymer will spread over the pigment's surfaceand good adhesion between the pigment and polymer will occur.

Prior art references teach the preparation of hydrophobic TiO₂ pigmentsby treatment with “non-reactive” organic substances, such aspolydimethylsiloxanes (see e.g., Noll, Chemie und Technologie derSilicon, 2nd ed., 1968, page 386 et seq.), polyorganosiloxanes (seee.g., U.S. Pat. No. 4,810,305) and phosphorylated fatty acid derivatives(see e.g., U.S. Pat. No. 4,209,430). These prior art, non-reactiveorganic substances interact with the metal oxide's surface partially orcompletely through Van Der Waals forces and/or electrostaticinteractions. Since these forces are comparatively weak, pigmentstreated with these organic substances may lose the coatings in laterprocessing stages or the organic substances may be extracted from thepigments during use.

The use of “reactive” organic compounds to modify the surface of metaloxide pigments is also well known. U.S. Pat. Nos. 4,061,503 and4,151,154 (both assigned to Union Carbide) disclose reactions oforganosilanes with TiO₂ to produce hydrophobic TiO₂ pigments whichenhance dispersibility in polymer matrices such as paints and plastics.In these patents the TiO₂ surface is treated with a silane possessing atleast two hydrolyzable groups bonded to the silicon and an organic groupcontaining a polyalkylene oxide group. The hydrolyzable groups aredescribed as alkoxys, such as methoxy and ethoxy. More specifically,U.S. Pat. No. 4,061,503 (which issued Dec. 6, 1977) describes the use ofa polyethyl substituted silicon compound having alkoxy-containinghydrolyzable groups with from about 1 to about 4 carbon atoms. U.S. Pat.No. 4,151,154 (which issued Apr. 24, 1979) also discloses the treatmentof titanium dioxide pigments with organosilicon compounds to improvedispersibility in polymers, similar to the '503 Patent, except itsclaims are directed to inorganic oxide particles generally and not justtitanium dioxide.

European Patent Application No. 492,223 (published Jul. 1, 1992)discloses the treatment of TiO₂ pigment with an organosilicon compoundhaving the formula R¹ R²R³R⁴Si wherein R¹ is a halogen or an alkoxyradical with 1 to 10 carbon atoms, R² is an alkyl group with 1 to 30carbons (preferably more than 8), and R³ and R⁴ are the same as eitherR¹ or R².

Great Britain Patent No. 1,154,835 (published Jun. 11, 1969) discloses aprocess for the treatment of finely divided materials, includingtitanium dioxide pigment. The patent indicates that inorganic powdersmay be rendered hydrophobic by treatment with organosilicon compounds.Specifically, the silicon compound has the formula R_(n)SiX_(4-n)wherein X is a halogen atom or a hydrolyzable alkoxy radical and R is amonovalent hydrocarbon radical (including an octyl [8 carbons] or anoctadecyl [18 carbons] radical) and n has the value of either 0 or 1.

Suzuki, et al., “Chemical Surface Treatment of Alumina, Titania, andTalc and Their Respective Surface Properties,” Shikizai, [J. Jap. Soc.Col. Mat.], Vol. 65, No. 2, pp. 59-67, 1992, describes the surfacetreatment of titania (large titanium dioxide crystals). As a comparison,the article refers to titanium dioxide particles that have been treatedwith octadecyltriethoxysilane—[the nonhydrolyzable group is octadecyl(18 carbons); the hydrolyzable groups are ethoxy]—to improve theparticles' dispersibility properties in organic solutions and solvents.

Union Carbide's A-137 Product Information brochure (copyrighted 1991)cites to a organosilane compound wherein the nonhydrolyzable group has 8carbons and the hydrolyzable group is ethoxy.

Great Britain Patent 785,393 discloses the treatment of TiO₂ pigmentwith organosilanes to improve uniformity of coloration and to reducestreaking in polymer matrices. Table 1 discloses the use ofnonyltriethoxysilane (the nonhydrolyzable group has 9 carbon atoms; thehydrolyzable group is ethoxy) and the use of ethyltrichlorosilane (thenonhydrolyzable group is ethyl; the hydrolyzable group is chloro).

Great Britain Patent 825,404 discloses a treatment of TiO₂ pigment toimprove dispersibility in organic solvents, including paint. In thepatent, the organosilanes are represented by the formulaR_(4-n)Si(OR¹)_(n) wherein R and R¹ represent alkyl, aryl, or a hydrogengroup. The preferred compounds include dimethyl-diethoxysilane,methyltriethoxysilane, ethyltriethoxysilane, and phenyltriethoxysilane.

U.S. Pat. No. 4,141,751 discloses the treatment of TiO₂ pigment with oneof three different agents to improve the pigment's dispersion propertiesin various polymers. In one embodiment, the agent is R-Si-X₃ wherein Rcan be an aliphatic or cycloaliphatic and X is a halogen or an alkoxygroup. Preferably, the treating agent is a methyltrimethoxysilane.

Recently, several PCT patent applications by DuPont have published inwhich organosilanes, similar to those disclosed in the above citedreferences, are used for surface treatment of TiO₂ pigment. For example,PCT patent publication WO 95/23192, published Aug. 31, 1995, disclosespolymer matrices containing silanized TiO₂ pigments in which a coatingon the pigments contains an organosilicon compound having the formula:

R_(x)Si(R¹)_(4-x,)

wherein R is a nonhydrolyzable aliphatic, cycloaliphatic or aromaticgroup having 8 to 20 carbon atoms; R¹ is a group selected from alkoxy,halogen, acetoxy or hydroxy or mixtures thereof; and x=1 to 3. Althoughhalogens are mentioned as suitable hydrolyzable groups, all examples andpreferred embodiments specify alkoxy groups. Specifically, thepublication discusses the use of octyltriethoxysilane—[thenonhydrolyzable group is octyl or 8 carbons; the hydrolyzable group isethoxy]. As obvious from the above discussion of the prior art, theDuPont patent application repeats various teachings already disclosed inthe Union Carbide patents and the other documents cited above.

DuPont's application WO 95/23194 discloses a process for preparingsilanized titanium dioxide pigments by media milling in which an aqueousslurry of the pigment is adjusted to pH 7.5 to 11, then treated with anorganosilicon reagent. The reagent is essentially the same as thatspecified in WO 95/23192, and preferably one which contains an alkoxyhydrolyzable group, such as methoxy or ethoxy.

DuPont's application WO 95/23195 discloses titanium dioxide pigmentswhich are treated with organosilicon compounds and boric acid or boronoxide. The boron ingredient can be dissolved in the organosiliconcompound and the admixture applied to the pigments by dry mixing or inan aqueous slurry. The organosilicon compound again preferably containsan hydrolyzable alkoxy group.

As can be seen from the above discussion, organoalkoxysilanes have beentraditionally used in the prior art for hydrophobizing inorganicpigments, such as TiO₂. A major deficiency of procedures that use alkoxysilanes is the generation of volatile organic compounds (VOC's), such asmethanol or ethanol, during hydrolysis of the silanes, according to theequation:

R-Si(OCH₂CH₃)₃+3H₂O→R-Si(OH)₃+3CH₃CH₂OH

Producers of minerals treated with organoalkoxysilanes are obligated toprotect their workers and the environment by collecting and disposing ofthese volatile organic compounds, which can often be expensive andtime-consuming. A further deficiency of utilizing alkoxyorganosilanes isthat under conditions encountered during processing and finishing thetreated pigments, a portion of the volatile alcohol can be converted tonoxious aldehydes. For example, ethanol can be oxidized to acetaldehydewhich can remain on the surface of the inorganic oxide and be subject toevolution during further processing of the inorganic oxide by theinorganic oxide producer or customer. Further, alkoxyorganosilanes areamong the most expensive organic materials known for hydrophobizingpigment surfaces.

Organohalosilanes are alternatives to organoalkoxysilanes for thetreatment of inorganic oxide pigments. However, since these compounds,particularly the organohalosilanes, react vigorously with moisture andwater, it would be expected that these reagents would have to be appliedto the inorganic oxides dry or using nonaqueous, organic media.

SUMMARY OF THE INVENTION

The present invention provides an environmentally safer process for theproduction of hydrophobic inorganic oxide products which comprisesreacting the inorganic oxide particles with condensation products fromorganohalosilanes, preferably organochlorosilanes, to producehydrophobic organosilane coated inorganic oxides. It is preferred thatthe organohalosilane compounds be reacted with the inorganic oxideparticles in an aqueous slurry under pH and mixing conditions sufficientto cause the desired reaction to take place.

The inorganic oxide pigments prepared by the processes of this inventionhave essentially quantitative retention of the organosilanes and containno adsorbed aldehydes on their surface, unlike pigments produced byprior art methods using organoalkoxysilanes, which are later released asvolatile organic compounds (VOC) in later stages of pigment processingor use. The by-products produced in the preferred embodiments of theinvention are innocuous salts, which are environmentally safe andreadily disposable.

DETAILED DESCRIPTION OF THE INVENTION

This invention provides hydrophobic inorganic oxide products which arefree of adsorbed aldehydes and other potentially volatile organiccompounds. The products of the present invention are produced by aprocess which overcomes the environmental deficiencies of prior artprocesses while, unexpectedly, maintaining or improving upon theprocessibility characteristics (e.g., dispersibility properties andlacing resistance) of such products in paints, plastics and othermaterials.

This section details the preferred embodiments of the subject invention.These embodiments are set forth to illustrate the invention, but are notto be construed as limiting. Since this disclosure is not a primer onthe manufacture of inorganic oxide products or pigments or theirtreatment with organosilane compounds, basic concepts known to thoseskilled in the art have not been set forth in detail. Concepts such aschoosing proper solvents or reaction conditions are readily determinableby those skilled in the art. Attention is directed to the appropriatetexts and references known to those in the art for details regardingacceptable temperatures, solvents, curing agents, etc.

Inorganic oxides appropriate for use in the present invention includethose which have surface hydroxyls capable of condensing with reactiveorganohalosilanes or condensates of organohalosilanes. Such inorganicoxides are represented by the rutile and anatase forms of titaniumdioxide, kaolin and other clays, alumina, silica, aluminum trihydrate,zirconium oxide, zinc oxide, iron oxide, cadmium pigments, chromatepigments, chromium oxide pigments, glass fibers, glass flake,wollastonite and the like. Preferred are standard pigment-grade titaniumdioxides, regardless of whether they have been obtained from titaniumtetrachloride or from titanium sulfate.

The inorganic oxide being coated with the condensates of theorganohalosilane can be an untreated inorganic oxide or an inorganicoxide whose surface has been treated by deposition thereon of phosphate,alumina, silica, zirconia and the like, using procedures well known topractitioners in the field of inorganic oxide surface treatment.

Suitable organohalosilanes for use in the present invention arerepresented by the formula

R_(n)SiX_(4-n)

where R represents a nonhydrolyzable aliphatic, cycloaliphatic oraromatic group (including saturated or unsaturated, branched orunbranched alkyl, aryl, cycloalkyl or alkylaryl groups) having from 1 to20 carbon atoms or a polyalkylene oxide group; X represents a halogenand n=1, 2, or 3.

For example, organochlorosilanes useful in this invention includebutyltrichlorosilane, hexyltrichlorosilane, octyltrichlorosilane,octylmethyldichlorosilane, decyltrichlorosilane, dodecyltrichlorosilane,tridecyltrichlorosilane, dihexyldichlorosilane, dioctyldichlorosilane,octadecyltrichlorosilane, and tributylchlorosilane. Preferredorganochlorosilanes have R groups with 4 to 10 carbons; most preferredare those with 6 to 8 carbons. Hexyltrichlorosilane andoctyltrichlorosilane are commercially and economically available andresult in organosilane-coated inorganic oxide pigments that haveexcellent dispersibility properties in plastics, and (particularly inthe case of hexyltrichlorosilane) produce pigmented plastics withexcellent lacing resistance.

The organohalosilanes can be employed in the invention individually oras mixtures of two or more species. The organohalosilane weight content,based upon the weight of the silanized inorganic oxide, is typicallyabout 0.1 to about 5.0%. For organochlorosilanes, the preferred weightcontent is about 0.1 to about 2% and most preferably about 0.5 to about1.5%.

The reacting of the inorganic oxide particles with the organohalosilanesin accordance with the invention may be accomplished by any suitablemethod by which surface treatment agents, coupling agents and the likeare supplied to particulate surfaces. Suitable methods include thoseknown to practitioners in the field of surface treatment of inorganicoxides, including the methods described in the prior art with respect tothe treatment of titanium dioxide pigment with organoalkoxysilanes(e.g., spraying the organohalosilanes onto the pigment or grinding theorganohalosilanes and pigment in a fluid energy mill). Suitable methodsalso include those utilized for the treatment of materials such assilicic fillers with organohalosilicon compounds.

However, it is preferred that the condensates of the organohalosilanesare reacted with the inorganic oxide pigments in an aqueous medium underacidic conditions. It has been surprisingly discovered that condensatesof the organohalosilanes can be made to react with inorganic oxides inaqueous environments if the admixture of the organohalosilanes and theinorganic oxide particles are subjected to intense mixing under acidicconditions.

The fact that condensates of the organohalosilanes can be made to reactwith inorganic oxides in an aqueous slurry is surprising sinceorganohalosilanes, particularly organochlorosilanes, react vigorouslywith moisture and water. Accordingly, it would have been expected thatthese substances must be applied to the inorganic oxides dry or usingnonaqueous, organic media. Conventional wisdom would predict that if theorganohalosilane was applied to inorganic oxides in an aqueous system,the organohalosilane would rapidly hydrolyze and form oligomers andpolymers that would not react with hydroxyl groups on the inorganicoxide's surface. See, e.g., Smith, A. L., Analytic History of Silicones,Wiley & Sons, 1991, pages 10-11, 29-30 and 256-257; Elvers, B. et. al.,Ullman's Encyclopedia Of Industrial Chemistry, 5th Ed., Vol. A 24(1993), pp. 30-31; and Goldschmidt et al., Silicones: Chemistry andTechnology, CRC Press, Boca Raton, Fla., 1991, pp. 98-99.

Unexpectedly, it has been found that condensates of theorganohalosilanes can be made to react with the surface of inorganicoxides in aqueous suspension by providing an acidic environment andsufficient mixing and curing. Although not wishing to be bound by aparticular theory or mechanism of operation, the inventors present thefollowing explanation to aid in an understanding of the invention.

When the titanium dioxide/organohalosilane reaction is conducted in anaqueous medium, the organohalosilane, e.g., octyltrichlorosilane, isadded to a treatment vessel containing a slurry composed ofpredominantly water with a small volume percentage of titanium dioxideparticles. If octyltrichlorosilane is added to pure water or to aneutral (non-acidic) water dispersion or slurry of titanium dioxide,there is an extremely fast reaction of octyltrichlorosilane forminghydrochloric acid and a sticky resin from the polymerization of thesilane portion of the octyltrichorosilane molecule. As noted in Smith,The Analytical Chemistry of Silicones, “One's first encounter withchlorosilanes is usually sufficient to instill a respect of theirreactivity. The briefest exposure to atmospheric moisture when loading asyringe and injecting a specimen into a chromatograph results in theevolution of hydrogen chloride [hydrochloric acid] and the appearance ofsiloxanes in the chromatogram.” p. 256.

Even though the titanium dioxide may be treated at solids levels of 500grams per liter of slurry or higher, the system is mostly water as thevolume occupied by the titanium dioxide particles is only about 8% ofthe system and that of water is about 92%. Consequently, asoctyltrichorosilane is added to the treatment vessel, the probability ofreacting with water is extremely high and quite low with respect to thetitanium dioxide.

It is contemplated that this aspect of the invention regarding thereaction of condensates of the organohalosilanes with inorganic oxidesin an aqueous system may be useful in fields outside of the treatment ofinorganic oxides. Materials (besides inorganic oxides) that arepresently treated with organohalosilanes in nonaqueous, organic mediamay be suitable for treatment in aqueous systems in accordance with thisdisclosure. Such treatment procedures may provide environmental and/orcost benefits such as the easy disposal of by-products, as discussedabove with respect to inorganic oxide treatment.

In a preferred embodiment of the invention, the organohalosilane isadded to a stirred, aqueous slurry of the inorganic oxide at a solidslevel of about 50 to 500 grams inorganic oxide per liter of water,preferably at a solids level of 300 to 400 grams per liter, at aninitial pH less than about 11, preferably less than about 7, mostpreferably between 2 and 6. The pH can be allowed to drift downward asthe organohalosilane is added or can be maintained at a desired value byadding base concurrently with the organohalosilane. The organohalosilanecan be added dropwise into the stirred slurry, pumped into the slurry orpumped into a slurry recirculation line or added by any other suitablemethod. The rate of organohalosilane addition is such that all of theorganohalosilane is added in about 1 minute to about 3 hours or longer,with a preferred addition time of 5 minutes to 1 hour and a mostpreferred addition time of about 10 minutes to about 45 minutes. Thetemperature of the organohalosilane treatment can be any suitabletreatment temperature up to approximately the boiling point of thewater. Preferably the treatment temperature is between 25 and 90° C.,and most preferably between 60 to 80° C.

Following treatment of the inorganic oxide, the slurry pH is adjusted toa desired value, typically between 2.0 and 8.0, more typically between4.0 and 6.0, preferably using sodium hydroxide, and the slurry isallowed to age with mixing for the time, preferably up to about 1 hour,required to assure equilibrium distribution of the components of theslurry.

Following aging, the pH of the slurry is adjusted to about 6.0 orgreater, preferably between about 6.0 to 9.0, and the organosilanecoated inorganic oxide is collected using filtration, centrifugation orany other suitable technique, washed to remove soluble impurities (suchas by-product salt), dried and further processed into a finished productusing techniques suitable for the specific inorganic oxide beingprocessed.

The use of organohalosilanes avoids formation of volatile organiccompounds, such as methanol and ethanol, which arise from the hydrolysisof traditional organoalkoxysilanes. The innocuous salts, such as sodiumchloride, which result from treatment of inorganic oxides withorganohalosilanes followed by neutralization, are easily disposed of anddo not pose a threat to the environment and health as do the volatilealcohols. In addition, the use of organohalosilanes eliminates theformation of noxious aldehydes which can form during inorganic oxidepigment processing. The noxious aldehydes can present an environmentalhazard during pigment preparation and residues can present a threatduring silanized pigment use in plastics applications.

The inorganic metal oxide pigments of this invention are unique in thatthey are not contaminated by measurable amounts of potentially hazardousoxidized by-products of prior art processes, e.g., aldehydes. Thehydrophobic inorganic oxide products of this invention offerprocessibility in polymer composites as least as good as pigmentsprepared according to prior art procedures; that is, the dispersibilityof the products of the present invention in polymers is at least as goodas prior art inorganic oxide pigments and the lacing resistance of theresulting polymer composites containing the products of the presentinvention is as good as prior art polymer composites. Representativepolymers in which the products of the present invention may be usedinclude, but are not limited to, polymers of ethylenically unsubstitutedmonomers, including polyethylene, polypropylene, polybutylene andcopolymers of ethylene with alpha-olefins containing 4 to 12 carbonatoms or vinyl acetate; vinyl homopolymers, acrylic homopolymers andcopolymers, polyamides, polycarbonates, polystyrenes,acrylonitrile-butadiene-styrenes, polyethers and the like.

The following examples set forth preferred embodiments of the invention.These embodiments are merely illustrative and are not intended to, andshould not be construed to, limit the claimed invention in any way.

EXAMPLES

Comparative Examples 1-4 demonstrate the metal oxide pigments treatedwith organotriethoxysilanes of the prior art contain associatedaldehydes while the pigments of the present invention do not.

Comparative Example 1

800 grams of neutral tone, chloride process, TiO₂ product containingabout 1.3% Al₂O₃ and about 0.15% P₂O₅ were slurried with 800 gramsdeionized water using a Rockwell Drill Press equipped with a 3 inchCowles blade, mixing at 2000 rpm. The slurry was transferred to a 2000ml glass beaker, heated to 80-85° C., and the slurry pH was adjustedfrom an initial pH of 5.9 to 4.5. While maintaining the slurry at about80° C. and with rapid stirring, 8.0 grams of octyltriethoxysilane(Prosil 9206 from PCR, Incorporated) was added. The treated slurry wasaged with rapid stirring for 30 minutes at 80-85° C. followed by ovendrying at 110° C. and micronization at 500° F. The micronized pigmentwas analyzed for acetaldehyde using gas chromatography/mass spectroscopyhead space analysis at 150° C. The acetaldehyde evolved from the pigmentis shown in Table 1.

Comparative Example 2

An octyltriethoxysilane treated pigment was prepared according to themethod of example 1 except the pH of the slurry during silane treatmentand aging was adjusted to 6.0. The micronized pigment was analyzed foracetaldehyde using gas chromatography/mass spectroscopy head spaceanalysis at 150° C. The acetaldehyde evolved from the pigment is shownin Table 1.

Comparative Example 3

An octyltriethoxysilane treated pigment was prepared according to themethod of example 1 except the pH of the slurry during silane treatmentand aging was adjusted to 7.0. The micronized pigment was analyzed foracetaldehyde using gas chromatography/mass spectroscopy head spaceanalysis at 150° C. The acetaldehyde evolved from the pigment is shownin Table 1.

Comparative Example 4

197.9 kilograms of a blue base chloride process TiO₂ rutile product wasmixed with deionized water so that the final volume of the slurriedproduct was 568.8 liters. The TiO₂ slurry was heated with continuousstirring at 60° C. Sufficient phosphoric acid was added to make thesystem acidic with a pH of 2.1. After a brief aging of 10 minutes, thepH of the slurry was adjusted with caustic to a pH of 5.0. Over a periodof 6 minutes 2,137 grams of octyltrichlorosilane was added to the slurryand the pH of the system was adjusted to 6.0 with caustic. Afterapproximately 90 minutes, the slurry was filtered, washed and dried inan oven. The dried octyltrichlorosilane-treated TiO₂ was deagglomeratedin a fluid energy mill with superheated steam at 240° C. The milledpigment was analyzed for acetaldehyde using gas chromatography/massspectroscopy head space analysis at 150° C. No acetaldehyde evolved froma sample of this pigment as shown in Table 1.

TABLE 1 Micrograms of Acetaldehyde Evolved at 150° C. per Gram of TiO₂Pigment Example 1 (Prior Art) 1.2 Example 2 (Prior Art) 1.5 Example 3(Prior Art) 2.4 Example 4 (This Invention) 0.0

The data in Table 1 show that the hydrophobic TiO₂ pigment product ofthis invention is clearly improved compared to pigments prepared usingorganotriethoxysilanes of the prior art. The pigment prepared accordingto this invention evolves no noxious acetaldehyde.

Preparation of Polyethylene Concentrates/Master Batches

50% TiO₂:50% polyethylene concentrates were prepared using a HaakeRheocord 9000 Computer Controlled Torque Rheometer. 125 g of TiO₂ and125 g of LDPE 722 manufactured by Dow Chemical Company were dry blendedand added to the 75° C. preheated chamber with rotors running at 50 rpm.One minute after addition of the TiO₂/LDPE mixture, the chambertemperature was raised to 105° C. Frictional heat generated by themixing process was allowed to drive the rate of incorporation of theTiO₂ into the LDPE until a steady state mixture was achieved.

75% TiO₂:25% polyethylene concentrates were prepared using a BR BanburyMixer. The mixer was preheated to 150° C. While the rotors were turning,313 grams of LDPE NA 209, manufactured by The Quantum Chemical Company,were added followed by 939 grams of TiO₂ which, in turn, was followed bythe remaining 313 grams of LDPE NA 209. The ram was lowered and set to50 psi. The point at which the two materials mix together and flux couldbe recognized by the ram bouncing up and down and an audible crackingsound. The material was allowed to mix for an additional 3 minutes afterflux before opening the mixer and allowing the material to discharge.This material was then cut into ˜1 inch pieces while hot. These pieceswere then placed into a Cumberland Crusher to obtain finely granulated75% concentrate samples.

The processibility of inorganic oxides into polymer composites can bejudged by evaluating the performance of the inorganic oxide under fourtest conditions, namely, extruder screen dispersion, melt flow, energyto achieve steady state flux and high temperature stability or lacingperformance. Each of these tests requires the use of TiO₂/polymerconcentrate of one of the types described above.

The extruder screen dispersion test measures how readily the TiO₂disperses in a polymer, e.g. low density polyethylene. 400 grams of a75% TiO₂ concentrate, prepared as described above, is extruded through aKillion 1″ extruder, followed by 1500 grams of LDPE, manufactured by TheChevron Chemical Company. The extruder temperatures are set at 350° F.(zone 1), 350° F. (zone 2), 390° F. (zone 3), and a screen packconfiguration of 100/400/200/100 mesh screens (from tip of extruderscrew to exit port for extrudate) is used. After all of the material hasextruded, the screen pack is removed, and the screens are stapled ontoan extrusion card. The screens are visually examined under a low powermicroscope (15×) and assigned screen ratings using standards. A ratingof 1 signifies “Best” and 5 “Worst.”

The fusion energy, or total torque required to achieve a steady statemixture of TiO₂ and polymer, under fixed process conditions, is also agood indicator of processibility. Fusion energy measurements tabulatedin Table 2 were obtained during production of 50 weight percent TiO₂concentrates in low density polyethylene using the procedure describedabove. The total torque required to achieve the steady state mixture isreadily obtainable during the production of the concentrates using thesoftware supplied with the Torque Rheometer. Lower fusion energy valuesindicate that the TiO₂ is more readily incorporated into the polymermatrix.

The melt index is another measure, albeit rather rough, indicator ofprocessibility. Melt flows are measured according to ASTM methodD1238-90b using 50% concentrates prepared according to the methoddescribed above. Higher melt indices imply easier processing.

Lacing is a measure of concentrate volatility at specific weight %pigment loadings and processing temperatures. Lacing tests wereconducted on 50% TiO₂ concentrate samples prepared according to themethod described above. The concentrates were conditioned for 48 hoursat 23° C. and 50% relative humidity. The concentrates were then let downinto LDPE 722 to achieve a 20% loading of TiO₂ in the final film.

Lacing evaluations were run on a 1″ Killion extruder equipped with aslot die for fabricating cast films. A temperature profile of 343°C./die, 288° C./adaptor, 232° C./zone 3, 190° C./zone 2, 148° C./zone 1was used. The screw speed was set at 90 rpm. A Killion 25.4 cm polishedchrome chill roll was used to cool and transport the films and was setto maintain a 75 μm film thickness. The chill roll distance from the dielips was 22 mm and the temperature was ˜27° C.

After the TiO₂/LDPE mix was placed in the hopper, the material wasallowed to run until the appearance of white in the clear film was firstnoted. To ensure the concentration of TiO₂ in the film had stabilized, atwo minute time interval was allowed before observations were recordedand a film sample taken. The extruder was then purged with LDPE untilthe film returned to clear.

Lacing performance was ranked by visual observations. Film samples werelaid out on a dark surface and ranked according to the relative size andnumber of holes. A 1.0-3.0 rating system was used. A rating of 1 wasgiven to films with no lacing, 2 was given to films showing the onset oflacing, and 3 was given to films with extreme lacing. Increments of 0.1were used to give some indication of relative performance between thesamples.

Comparative examples 5-8 demonstrate that pigments prepared according tothe teachings of this invention maintain equal or improvedprocessibility in polyethylene compared to prior art pigments. This isaccomplished in conjunction with the reduced environmental threats ofthe present inventive process. The pigments of examples 5-8 wereprepared in full scale production facilities. Comparisons are maderealizing that many factors can influence variability in productionprocesses. Statistical process control techniques were used to minimizevariability in the production processes.

Comparative Example 5

Optimized, state-of-the-art production technology was used to prepare ahydrophobic TiO₂ pigment using polydimethysiloxane as a treatment forhydrophobizing the TiO₂. The pigment was tested in polyethylene forscreen dispersion, energy required to mix with polyethylene, melt flowand lacing performance. The results are summarized in Table 2.

Comparative Example 6

Optimized, state-of-the-art production technology was used to prepare ahydrophobic TiO₂ pigment using Sylvacote K, a phosphorylated fatty acidderivative, as a treatment of hydrophobizing the TiO₂. The pigment wastested in polyethylene for screen dispersion, energy required to mixwith polyethylene, melt flow and lacing performance. The results aresummarized in Table 2.

Comparative Example 7

Optimized, state-of-the-art production technology was used to prepare ahydrophobic TiO₂ pigment using octyltriethoxysilane as a treatment forhydrophobizing the TiO₂. The pigment was tested in polyethylene forscreen dispersion, energy required to mix with polyethylene, melt flowand lacing performance. The results are summarized in Table 2.

Comparative Example 8

Optimized, state-of-the-art production technology was used to prepare ahydrophobic TiO₂ pigment using octyltrichlorosilane as a treatment forhydrophobizing the TiO₂. The pigment was tested in polyethylene forscreen dispersion, energy required to mix with polyethylene, melt flowand lacing performance. The results are summarized in Table 2.

Comparative Example 9

Optimized, state-of-the-art production technology was used to prepare ahydrophobic TiO₂ pigment using hexyltrichlorosilane as a treatment forhydrophobizing the TiO₂. The pigment was tested in polyethylene forscreen dispersion, energy required to mix with polyethylene, melt flowand lacing performance. The results are summarized in Table 2.

TABLE 2 Processibility Parameters of Hydrophobic TiO₂ Pigments ScreenFusion Energy Melt Flow Dispersion (m.Kg.M) (g/10 min) Lacing Example 52 15.4 5.5 2.0 (prior art) Example 6 1 10.7 5.3 1.7 (prior art) Example7 1 14.3 5.2 1.6 (prior art) Example 8 1 10.2 5.7 1.6 (this invention)Example 9 1 14.0 5.7 1.1 (this invention)

The data in Table 2 show that a TiO₂ pigment of this invention providesfor processing in polyethylene at least as well as optimized TiO₂pigments made according to prior art. This is accomplished inconjunction with the reduced environmental threats of the presentinventive process.

Upon reading the subject application, various alternative constructionsand embodiments will become obvious to those skilled in the art. Thesevariations are to be considered within the scope and spirit of thesubject invention. The subject invention is only to be limited by theclaims which follow and their equivalents.

We claim:
 1. A process for producing a silanized inorganic oxide pigment which comprises adding an inorganic oxide and an organohalosilane represented by the formula R_(n)SiX_(4-n) where R represents a nonhydrolyzable aliphatic, cycloaliphatic or aromatic group having from 1 to 20 carbon atoms or a polyalkylene oxide group; X represents a halogen and n=1, 2, or 3; to an aqueous media so as to form a slurry, and subjecting the slurry to intense mixing so as to produce a silanized inorganic oxide pigment having a coating formed through a chemical reaction.
 2. The process of claim 1 in which the organohalosilane is an organochlorosilane.
 3. The process of claim 1 in which R has 4 to 10 carbon atoms.
 4. The process of claim 3 in which R has 6 to 8 carbon atoms.
 5. The process of claim 2 in which the organochlorosilane is octyltrichlorosilane or hexyltrichlorosilane or mixtures thereof.
 6. The process of claim 1 in which the inorganic oxide is titanium dioxide.
 7. The process of claim 5 in which the inorganic oxide is titanium dioxide.
 8. The process of claim 1 in which the inorganic oxide is selected from the group consisting of zinc oxide, aluminum oxide, silicon dioxide, zirconium oxide, lithipone, lead oxide, chromium oxide pigments, iron oxide pigments and cadmium pigments.
 9. The process of claim 1 wherein said intense mixing is at a level sufficient to achieve equilibrium distribution of the organohalosilane throughout the slurry.
 10. The process of claim 1 which further comprises adjusting the slurry to acidic pH conditions during the adding step, aging the slurry, neutralizing any acid that may evolve, and recovering the silanized inorganic oxide pigment from the slurry.
 11. The process according to claim 10 in which the pH of the slurry is initially between 2 and
 6. 12. The process according to claim 11 in which the organohalosilane is added over a time period between about 10 minutes and about 45 minutes.
 13. The process according to claim 1 in which the slurry is at to a temperature between 60 and 80° C.
 14. The process according to claim 10 in which the pH during the aging of the slurry is between about 2 and about
 7. 15. The process according to claim 10 in which the slurry is aged for sufficient time to achieve equilibrium distribution of the organohalosilane and the inorganic oxide.
 16. The process according to claim 10 in which the slurry is neutralized to a pH of between about 6.0 to about 9.0.
 17. The process according to claim 10 in which the silanized inorganic oxide pigment is wet ground or dry ground.
 18. The process of claim 10, wherein the organohalosilane is a mixture of two or more organohalosilanes independently represented by the formula R_(n)SiX_(4-n) where R represents a nonhydrolyzable aliphatic, cycloaliphatic or aromatic group having 5-10 carbon atoms or a polyalkylene oxide group.
 19. A process of claim 1, wherein the inorganic oxide is added to the aqueous media prior to the addition of the organohalosilane.
 20. A silanized inorganic oxide pigment produced by the process of claim
 1. 21. A silanized inorganic oxide pigment produced by the process of claim
 10. 22. A composite comprising a polymer and a silanized inorganic pigment wherein the pigment is produced by the process of claim
 1. 23. A polymer composite containing the pigment of claim
 20. 